This invention relates to railcars and, more particularly, to so-called "intermodal" flatcars which are used to carry containers, trailers, or both.
As a result of increasing fuel costs and other factors, the shipping and trucking industries are resorting to the use of more economical 45 foot containers and 45 foot trailers and are, in some instances, considering replacement of entire fleets of conventional 40 foot trailers. However, the typical intermodal flatcar, which is either 85 feet or 89 feet in length over end sills, cannot readily carry two 45 foot containers or trailers economically. More specifically, an 89 foot flatcar can carry only one 40 foot trailer and one 45 foot trailer simulataneously, as depicted in FIG. 10. With this equipment, therefore, the railroad must carry an equal mix of 40 and 45 foot trailers on its 89 foot flatcars, and either a single 45 foot trailer or two 40 foot trailers on its 85 foot flatcars, and similarily for containers. However, the increasing number of 45 foot trailers in use or entering use often makes it difficult or impossible to obtain an economical mix of 40 and 45 foot trailers at the time a train is made up. As a consequence, the railroad often makes up the train with several 85 or 89 foot flatcars each carrying only a single 45 foot trailer. This results in several economic penalties, among which are: unused load carrying capacity of the available equipment; reduced net/tare ratio; and increased maintenance-of-way per net ton and fuel costs due to the low net-to-tare weight ratio and aerodynamic drag created by the gap between trailers on adjacent flatcars.
Accordingly, there is an urgent need for an intermodal flatcar that can carry 45 foot, or larger, trailers or containers economically. The railroad industry, however, is in a dilemma since it cannot afford to scrap its current fleet of approximately 60,000 intermodal flatcars in favor of buying new equipment designed specifically for 45 foot trailers. Further, since many of these flatcars still possess substantial useful life, the railroad industry is reluctant to invest substantial sums in new equipment until the useful life of its current equipment approaches an end.
Modification or retrofitting of existing intermodal flatcars to make them more economical has not been satisfactory, relocating container pedestals, or the trailer hitches, so as to accept two 45 foot trailers is not desirable because typical 45 foot trailers may overhang the strikers, as depicted in FIG. 11. Likewise, it would not be possible to carry two 45 foot trailers having nose refrigeration units due to the lack of sufficient clearance between these units and the rear of the preceeding trailer. Further, no reduction in net/tare ratio would be obtained, and extra handling costs would be incurred because of more precise trailer positioning.
Another such modification is aimed at reducing the weight of the standard 85 foot or 89 foot flatcar simply by removing portions of the deck structure. This has been found to be impractical because the original beam strength of the flatcar would be weakened excessively. In a typical 89 foot flatcar, for example, the loss of deck structure, which tends to act as a beam flange to the center beam, would overload the remaining center beam structure such that it could not withstand the combined loads as defined in paragraph 4.2.2.7 in Section C-II of the AAR Manual, (1.8 times vertical dead load, live load and draft load; and 1.5 times lateral load). In this case the maximum compressive stress level in the typical center beam would be approximately 96,000 psi, far above its material yield strength of either 46,500 or 50,000 psi, depending upon the type and thicknesses of steel used.
The extreme length of the existing intermodal flatcars also mitigates against their continued use. Beam deflection problems require that many such flatcars be "starred" or down rated at a load carrying capacity which is from 2,000 to 27,000 pounds less than their actual AAR determined carrying capacity. This is in large part due to lack of rail clearance when the beam structure is at maximum deflection, or on vertical curves. These cars also suffer from operational drawbacks in that they have difficulty negotiating curves, a condition also causing severe derailment problems when run empty, especially at the head end of the train.